Personally, I don't use or recommend using either. Instead, use a sharp pair of trimming scissors and cut pcs as fine as possible, then scrape any resin on the blades in with the chopped buds.
A food processor could work if you're careful and don't chop the buds too much but you'll end up leaving trichs in the processor. The coffee maker is much worse because it will powder everything which will probably make your cannabutter much more green and tasting like the plant.
So personally I prefer scissors because you have better control and fewer wasted trichs.